Turners syndrome

Turner syndrome is a chromosomal disorder that affects females, characterized by the partial or complete loss of one X chromosome. It is associated with a range of physical, endocrine, and reproductive abnormalities. Early recognition and management are important to improve growth, development, and long-term health outcomes.

Definition and Genetics

Turner syndrome is defined as a condition in which females have complete or partial absence of one X chromosome, leading to a variety of clinical manifestations.

• Chromosomal abnormalities:
  • Monosomy X (45,X): Complete absence of one X chromosome, the most common form of Turner syndrome.
  • Mosaicism (45,X/46,XX or other variants): Presence of two or more different cell lines with varying X chromosome content.
  • Structural abnormalities: Includes isochromosomes, ring chromosomes, and deletions affecting X chromosome function.
• Inheritance patterns and sporadic occurrence: Turner syndrome usually occurs sporadically due to nondisjunction during gametogenesis; familial inheritance is rare.

Pathophysiology

The clinical manifestations of Turner syndrome arise from the loss of genetic material on the X chromosome, which affects multiple organ systems.

• Effects of X chromosome monosomy on development: Disruption of genes involved in growth, skeletal development, and ovarian function.
• Hormonal and endocrine dysfunctions: Ovarian dysgenesis leads to estrogen deficiency and altered levels of follicle-stimulating hormone (FSH) and luteinizing hormone (LH).
• Impact on growth, ovarian function, and cardiovascular system: Short stature, delayed or absent puberty, and increased risk of congenital heart defects such as bicuspid aortic valve and coarctation of the aorta.

Clinical Features

Turner syndrome presents with a combination of physical, reproductive, cardiovascular, and endocrine features. The severity and combination of features can vary depending on the karyotype.

• Physical characteristics:
  • Short stature
  • Webbed neck and low hairline
  • Cubitus valgus and broad chest with widely spaced nipples
  • Edema of hands and feet in infancy
• Gonadal and reproductive features:
  • Ovarian dysgenesis leading to primary amenorrhea
  • Infertility due to premature ovarian failure
• Cardiovascular abnormalities:
  • Coarctation of the aorta
  • Bicuspid aortic valve
• Renal anomalies: Horseshoe kidney and other structural abnormalities
• Endocrine and metabolic disorders:
  • Hypothyroidism
  • Increased risk of glucose intolerance and diabetes
• Other features:
  • Hearing loss
  • Ocular abnormalities such as strabismus
  • Cognitive and neuropsychological profile with normal intelligence but specific learning difficulties

Diagnostic Evaluation

Diagnosis of Turner syndrome involves a combination of clinical assessment, laboratory testing, and imaging studies to confirm chromosomal abnormalities and detect associated anomalies.

Clinical Assessment

• Growth charts and physical examination to detect short stature and characteristic features
• Identification of phenotypic features such as webbed neck, broad chest, and limb abnormalities

Laboratory Investigations

• Karyotyping for chromosomal analysis to confirm monosomy X or mosaicism
• Hormonal assays including FSH, LH, and estrogen levels to assess ovarian function
• Thyroid function tests to detect hypothyroidism

Imaging Studies

• Ultrasound of ovaries and uterus to evaluate gonadal development
• Echocardiography to detect congenital heart anomalies such as bicuspid aortic valve
• Renal ultrasound to identify structural anomalies such as horseshoe kidney

Differential Diagnosis

Several conditions can present with features similar to Turner syndrome, and should be considered during evaluation to ensure accurate diagnosis.

• Noonan syndrome: Characterized by short stature, webbed neck, and congenital heart defects, but typically normal female karyotype.
• Other causes of primary amenorrhea and short stature:
  • Congenital adrenal hyperplasia
  • Hypogonadotropic hypogonadism
  • Other chromosomal abnormalities such as mosaic 46,XY gonadal dysgenesis

Management and Treatment

Management of Turner syndrome requires a multidisciplinary approach to address growth, hormonal deficiencies, cardiovascular risks, reproductive health, and psychosocial support.

Growth and Hormonal Therapy

• Growth hormone therapy to improve final adult height
• Estrogen replacement therapy to initiate and maintain secondary sexual characteristics
• Progesterone therapy to induce cyclic menstruation once estrogen therapy is established

Cardiovascular Management

• Regular monitoring for congenital heart defects and aortic dilation
• Surgical interventions for coarctation of the aorta or significant valve abnormalities

Fertility and Reproductive Options

• Assisted reproductive technologies, including egg donation and in vitro fertilization
• Preconception counseling for cardiovascular and endocrine risks

Psychosocial Support

• Genetic counseling for patients and families
• Educational and behavioral support for cognitive or learning difficulties

Prognosis and Complications

The prognosis of Turner syndrome has improved with early diagnosis and multidisciplinary care. However, patients remain at risk for several long-term complications.

• Impact on life expectancy: Slightly reduced due to cardiovascular complications and associated comorbidities.
• Risk of cardiovascular events: Increased risk of aortic dissection, hypertension, and ischemic heart disease.
• Reproductive challenges: Infertility due to ovarian failure and primary amenorrhea.
• Endocrine and metabolic complications: Hypothyroidism, glucose intolerance, and increased risk of type 2 diabetes.
• Other complications: Osteoporosis due to estrogen deficiency, hearing loss, and psychosocial issues related to short stature or infertility.

Prevention and Genetic Counseling

While Turner syndrome cannot be prevented, early diagnosis and genetic counseling help manage the condition and reduce complications.

• Importance of early diagnosis: Enables timely initiation of growth hormone and estrogen therapy, improving outcomes.
• Family planning and reproductive options: Genetic counseling informs patients about fertility options, assisted reproductive technologies, and prenatal considerations.
• Screening for associated anomalies: Regular cardiovascular, renal, and endocrine evaluations to detect and manage complications early.
• Patient education: Guidance on lifestyle modifications, adherence to therapy, and awareness of potential health risks.

References

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9. Stochholm K, Juul S, Juel K, et al. Prevalence, incidence, diagnostic delay, and mortality in Turner syndrome. J Clin Endocrinol Metab. 2006;91(10):3897-3902.